The present invention relates generally to cast gas turbine engine components and their method of manufacture. More particularly, in one embodiment of the present invention, a multi-airfoil vane segment is produced as a single crystal casting from a Rhenium containing directionally solidified (DS) chemistry alloy. Although the invention was developed for gas turbine engine components, certain applications may be outside of this field.
The performance of a gas turbine engine generally increases with an increase in the operating temperature of a high temperature working fluid flowing from a combustion chamber. One factor recognized by gas turbine engine designers as limiting the allowable temperature of the working fluid is the capability of the engine components to not degrade when exposed to the high temperature working fluid. The airfoils, such as blades and vanes, within the engine are among the components exposed to significant thermal and kinetic loading during engine operation.
Many gas turbine engines utilize cast components formed of a nickel or cobalt alloy. The components can be cast as a polycrystalline, directionally solidified, or single crystal structure. Generally, the most desirable material properties are associated with the single crystal structure. However, the geometry of some components, such as the multi-airfoil vane segment, causes difficulty during the casting process largely associated with grain or crystal defects. Single crystal alloys are not tolerant to these types of defects and therefore castings, which exhibit these defects, are generally not suitable for engine use. Thus, the casting yields are lower and consequently the cost to manufacture the component increases.
A directionally solidified component has material properties between single crystal and polycrystalline and are easier to produce than single crystal components. Directionally solidified components are generally defined as multi-crystal structures with columnar grains and are generally cast from a directionally solidified alloy containing grain boundary strengtheners. The directionally solidified component is best suited for designs where the stress field is oriented along the columnar grains and the stress field transverse to the columnar grain is minimized. However, in a component, such as a multi-airfoil vane segment, the stress fields are elevated along the airfoils and in a transverse direction associated the inner and outer shrouds which tie the airfoils together.
Although the prior techniques can produce single crystal multi-airfoil vane segments, there remains a need for an improved single crystal multi-airfoil vane segment and method of manufacture. The present invention satisfies this and other needs in a novel and unobvious way.
One form of the present invention contemplates a product comprising a cast single crystal structure formed of a directionally solidified alloy.
Another form of the present invention contemplates a gas turbine engine component, comprising a single cast single crystal vane segment having a plurality of airfoils, the vane segment is formed of a directionally solidified alloy.
Yet another form of the present invention contemplates a gas turbine engine component comprising a single cast single crystal shrouded vane formed of a directionally solidified alloy.
Also, another form of the present invention contemplates a method for producing a single crystal article. The method comprising: providing a directionally solidified alloy; melting the directionally solidified alloy; pouring the molten directionally solidified alloy into a casting mold; and, solidifying the directionally solidified alloy to produce a single crystal article.
One object of the present invention is to provide a single crystal multi-airfoil vane segment and method of manufacture.
Related objects and advantages of the present invention will be apparent from the following description.